Add spec directory for each IBC client implementation

[colin-axner]

Summary

Add a spec directory for each IBC client implementation.

• solo machine
• tendermint
• localhost

Problem Definition

Clients can be very complex in verification logic and our IBC implementation can very in small details from the ICS spec while still being valid. We should be clearly documenting in words the behaviour of each client.

Proposal

Add a spec directory for each client (tendermint, localhost, solo machine). This can be done now or as we move clients in a light-clients directory.

Some specific things to be mentioned:

Tendermint (TODO: add from previous prs - validator set hash change, removal of signed header)

Localhost

• comment
• comment

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[colin-axner]

I'll be working on solo machine docs next week

[colin-axner]

Moved from cosmos/cosmos-sdk#6134: Document how to connect to localhost client to relay and test messages

[colin-axner]

The spec should be moved to docs as per #135

There should be 07-tendermint docs, but that should be a separate issue and isn't high priority (light client dev guide would be higher priority)